Valve timing adjusting apparatus

ABSTRACT

A valve timing adjusting apparatus includes a driving-side rotor, a driven-side rotor, and a directional control valve. The driven-side rotor is rotated in the advance direction when the advance and retard output ports communicate with the intake port and the retard drain port respectively, and the advance and retard output ports are disconnected from the advance drain port. The driven-side rotor is rotated in the retard direction when the advance and retard output ports communicate with the advance drain port and the intake port respectively, and the advance and retard output ports are disconnected from the retard drain port. A relay passage is provided at an exterior of the directional control valve for communication with the advance and retard drain ports. The drain relay passage closes the advance and retard drain ports relative to the exterior.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-84525 filed on Mar. 27, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve timing control apparatus for controlling valve timing of a valve that is opened and closed by a camshaft through torque transmitted from a crankshaft in an internal combustion engine.

2. Description of Related Art

A conventional fluid-actuated valve timing adjusting apparatus is commonly known to includes a housing and a vane rotor. The housing serves as a driving-side rotor that is rotatable synchronously with a crankshaft, and the vane rotor serves as a driven-side rotor that is rotatable synchronously with a camshaft. For example, JP-A-2002-235513 (FIGS. 9, 10) corresponding to US2002/0088413 (FIGS. 8, 9) discloses an apparatus that defines an advance chamber and a retard chamber arranged in a rotational direction one after another between the housing and the vane rotor. In the apparatus of JP-A-2002-235513, supply of working fluid to the advance chamber or to the retard chamber rotates the vane rotor relative to the housing in an advance direction or a retard direction in order to adjust valve timing.

In the apparatus of JP-A-2002-235513, a directional control valve and a check valve serve as a control unit that controls supply of working fluid to the advance chamber and the retard chamber. More specifically, the directional control valve includes an intake port, an advance output port, a retard output port, an advance drain port, and a retard drain port. The directional control valve receives working fluid from a fluid input source through the intake port, and outputs working fluid to the advance chamber and the retard chamber through the advance output port and the retard output port, respectively. Also, the directional control valve drains working fluid to the exterior through the advance drain port and the retard drain port. Then, the directional control valve has a relay passage that connects the advance drain port with the retard drain port. Also, the directional control valve has a communication passage that branches from the relay passage and that is communicated with the intake port. The check valve is provided in the above communication passage.

In the apparatus of JP-A-2002-235513, in order to rotate the vane rotor relative to the housing, for example, in an advance direction, the advance output port is communicated with the retard output port is communicated with the retard drain port in the directional control valve. Also, simultaneously, in the directional control valve, the advance output port and the retard output port are both disconnected from the advance drain port.

In the above, torque variations (torque reversals) are applied to the vane rotor from the camshaft alternately in the advance and retard directions relative to the housing The torque applied in the advance direction corresponds to a negative torque, and the torque applied in the retard direction corresponds to a positive torque in the present specification, for example. When the negative torque is applied to the vane rotor through the camshaft, the retard chamber is compressed, and thereby working fluid in the retard chamber is drained to the retard drain port through the retard output port. The fluid drained to the retard drain port flows into the relay passage and the communication passage sequentially, and accordingly the check valve is opened. As a result, the drained fluid is outputted to the advance chamber from the intake port through the advance output port. As a result, because it is possible to supply the fluid drained from the retard chamber to the advance chamber that is increased in volume due to the above negative torque, it is possible to increase a rotational speed of the vane rotor relative to the housing in the advance direction. In other words, it is possible to improve the response speed in the timing advance operation.

Also, in a case, where the ports of the directional control valve are communicated with each other in the above communication/discommunication state, if the positive torque is applied to the vane rotor in the retard direction through the camshaft, the advance chamber is compressed accordingly. Thus, working fluid in the advance chamber is drained to the intake port through the advance output port. Fluid drained to the intake port flows into the communication passage, and accordingly the check valve is closed. As a result, flow of the drained fluid into the relay passage is limited. Generally, when the vane rotor is rotated in the advance direction, fluid in the retard chamber is required to be drained However, the fluid in the advance chamber is drained disadvantageously if the positive torque is applied to the vane rotor in the retard direction even while the vane rotor is rotated in the advance direction. In the conventional art, the check valve is capable of limiting the backflow of the drained fluid from the advance chamber to the retard chamber through the relay passage, the retard drain port, and the retard output port. Thus, the backflow of fluid to the retard chamber is limited as above, and thereby the unwanted rotation of the vane rotor relative to the housing in the retard direction is limited. As a result, it is possible to avoid the deterioration of timing advance responsivity.

In the apparatus of JP-A-2002-235513, it is possible to achieve high timing retard responsivity also in a case, where the vane rotor is rotated relative to the housing in the retard direction by the mechanism similar to the above timing advance case.

In the apparatus of JP-A-2002-235513 (FIGS. 9, 10), in order to improve the timing advance responsivity and the timing retard responsivity, it is important to increase a passage area or a cross sectional area of the communication passage such that an amount of supplied working fluid while the check valve opens is increased. However, when the area of the communication passage is increased, a valve element of the check valve provided in the communication passage is increased in size, accordingly. As a result, pressure drop of working fluid that flows through the opened check valve is substantially enhanced, and thereby the timing advance responsivity and the timing retard responsivity may deteriorate disadvantageously.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.

To achieve the objective of the present invention, there is provided a valve timing adjusting apparatus for adjusting valve timing of a valve that is opened and closed by a camshaft through torque transmission from a crankshaft of an internal combustion engine, the valve timing adjusting apparatus including a driving-side rotor, a driven-side rotor, and a control unit. The driving-side rotor is rotatable synchronously with the crankshaft. The driven-side rotor is rotatable synchronously with the camshaft. The driven-side rotor and the driving-side rotor define therebetween an advance chamber and a retard chamber arranged one after another in a rotational direction. When working fluid is supplied to the advance chamber or the retard chamber, the driven-side rotor is rotated relative to the driving-side rotor in an advance direction or a retard direction. The control unit controls supply of working fluid to the advance chamber and the retard chamber. The control unit includes a directional control valve, an advance communication passage, an advance check valve, a retard communication passage, a retard check valve, and a drain relay passage. The directional control valve includes an intake port, an advance output port, a retard output port, an advance drain port, and a retard drain port. The directional control valve receives working fluid from an external fluid input source through the intake port. The directional control valve outputs working fluid to the advance chamber through the advance output port. The directional control valve outputs working fluid to the retard chamber through the retard output port. The directional control valve drains working fluid through the advance drain port. The directional control valve drains working fluid through the retard drain port. The driven-side rotor is rotated relative to the driving-side rotor in the advance direction when the followings are satisfied; the directional control valve provides communication between the advance output port and the intake port, the directional control valve provides communication between the retard output port and the retard drain port, and the directional control valve disconnects the advance output port and the retard output port from the advance drain port. The driven-side rotor is rotated relative to the driving-side rotor in the retard direction when the followings are satisfied; the directional control valve provides communication between the advance output port and the advance drain port, the directional control valve provides communication between the retard output port and the intake port, and the directional control valve disconnects the advance output port and the retard output port from the retard drain port. The advance communication passage is provided at an exterior of the directional control valve and is communicated with the advance drain port and the intake port. The advance communication passage closes the advance drain port and the intake port relative to the exterior of the directional control valve. The advance check valve is provided in the advance communication passage. The advance check valve allows working fluid to flow from the advance drain port toward the intake port and limits working fluid from flowing from the intake port toward the advance drain port. The retard communication passage is provided at the exterior of the directional control valve and is communicated with the retard drain port and the intake port. The retard communication passage closes the retard drain port and the intake port relative to the exterior of the directional control valve. The retard check valve is provided in the retard communication passage. The retard check valve allows working fluid to flow from the retard drain port toward the intake port and limits working fluid from flowing from the intake port toward the retard drain port. The drain relay passage is provided at the exterior of the directional control valve and is communicated with the advance drain port and the retard drain port. The drain relay passage closes the advance drain port and the retard drain port relative to the exterior of the directional control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a configuration diagram illustrating a valve timing adjusting apparatus according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1;

FIG. 3 is a schematic diagram for explaining torque variations applied to a drive unit of valve timing adjusting apparatus according to the one embodiment of the present invention;

FIG. 4 is a cross-sectional view schematically illustrating a detailed configuration and an operational state of a control unit of the valve timing adjusting apparatus according to the one embodiment of the present invention;

FIG. 5 is a cross-sectional view schematically illustrating an operational state of the control unit in FIG. 4;

FIG. 6 is a cross-sectional view schematically illustrating an operational state of the control unit in FIG. 4;

FIG. 7 is a cross-sectional view schematically illustrating an operational state of the control unit in FIG. 4, and

FIG. 8 is a cross-sectional view schematically illustrating an operational state of the control unit in FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One embodiment of the present invention will be described with reference to accompanying drawings.

FIG. 1 shows an example, in which a valve timing adjusting apparatus 1 of one embodiment of the present invention is applied to an internal combustion engine of a vehicle. The valve timing adjusting apparatus 1 is a fluid-actuated apparatus employing hydraulic oil serving as “working fluid” and adjusts valve timing of an intake valve that serves as “a valve”.

(Basic Configuration)

Basic configuration of the valve timing adjusting apparatus 1 will be described below. As shown in FIGS. 1, 2, the valve timing adjusting apparatus 1 includes a drive unit 10 and a control unit 30. The drive unit 10 is provided to a transmission system that transmits an engine torque of a crankshaft (not shown) of the internal combustion engine to a camshaft 2 of the internal combustion engine, and is driven by hydraulic oil. The control unit 30 controls supply of hydraulic oil to the drive unit 10.

(Drive Unit)

The drive unit 10 includes a housing 11 serving as a “driving-side rotor” and a vane rotor 14 serving as a “driven-side rotor”. The housing 11 has a shoe housing 12, a sprocket 13, and a front plate 18. The shoe housing 12 has a tubular portion 12 a and shoes 12 b, 12 c, 12 d, 12 e. The tubular portion 12 a has a hollow cylindrical shape, and the shoes 12 b, 12 c, 12 d, 12 e serve as section portions. Each of the shoes 12 b to 12 e is arranged at the tubular portion 12 a one after another in a rotational direction at equal intervals therebetween and projects from the tubular portion 12 a in a radially inner direction. Each of the shoes 12 b to 12 e has a radially inner surface having an arcuate shape taken by a plane perpendicular to the rotational axis of the vane rotor 14. A hub portion 14 a of the vane rotor 14 has an outer peripheral surface that is in contact with the radially inner surface of each of the shoes 12 b to 12 e. A receiving chamber 50 is defined between adjacent ones of the shoes 12 b to 12 e in the rotational direction.

Each of the sprocket 13 and the front plate 18 has an annular plate shape, and the sprocket 13 and the front plate 18 are fixed coaxially to the shoe housing 12 at opposite axial ends of the shoe housing 12. The sprocket 13 is coupled to the crankshaft through a timing chain (not shown). Thus, during an operation of the internal combustion engine, the housing 11 rotates synchronously with the crankshaft in a clockwise direction in FIG. 1 because of the transmission of the engine torque from the crankshaft to the sprocket 13.

As shown in FIGS. 1, 2, the housing 11 of the drive unit 10 coaxially receives therein the vane rotor 14, and the housing 11 contacts the vane rotor 14 in a longitudinal direction. The vane rotor 14 includes the hub portion 14 a having a hollow cylindrical shape and vanes 14 b, 14 c, 14 d, 14 e. The hub portion 14 a is fixed coaxially to the camshaft 2 through a bolt. Due to the above configuration, the vane rotor 14 is rotatable synchronously with the camshaft 2 in the clockwise direction in FIG. 1, and is rotatable relative to the housing 11. Each of the vane 14 b to 14 e is arranged at the hub portion 14 a one after another in the rotational direction at equal intervals and projects from the hub portion 14 a in the radially outer direction. Thus, each of the vane 14 b to 14 e is received in the corresponding receiving chamber 50. Each of the vane 14 b to 14 e has a radially outer surface having an arcuate cross sectional shape taken by a plane perpendicular to the rotational axis of the vane rotor 14. The radially outer surface slides on an inner peripheral surface of the tubular portion 12 a.

Each of the vane 14 b to 14 e divides the corresponding receiving chamber 50 into two chambers. More specifically, each of the vane 14 b to 14 e and the housing 11 define therebetween an advance chamber and a retard chamber serving as fluid chambers For example, an advance chamber 52 is defined between the shoe 12 b and the vane 14 b, an advance chamber 53 is defined between the shoe 12 c and the vane 14 c, an advance chamber 54 is defined between the shoe 12 d and the vane 14 d, and an advance chamber 55 is defined between the shoe 12 e and the vane 14 e. Also, a retard chamber 56 is defined between the shoe 12 c and the vane 14 b, a retard chamber 57 is defined between the shoe 12 d and the vane 14 c, a retard chamber 58 is defined between the shoe 12 e and the vane 14 d, and a retard chamber 59 is defined between the shoe 12 b and the vane 14 e.

The vane 14 b receives a lock pin 26. The lock pin 26 is displaceable by a restoring force of a compression coil spring 28, and is fitted into a fitting hole 27 of the sprocket 13 by the displacement. As a result, the lock pin 26 locks the vane rotor 14 relative to the housing 11. In the present embodiment, in a state, where a relative rotational position of the vane rotor 14 relative to the housing 11 corresponds to a full retard position (see FIG. 1), the lock pin 26 is capable of locking the vane rotor 14 relative to the housing 11. It should be noted that the lock pin 26 is capable of unlock the vane rotor 14 relative to the housing 11 when the lock pin 26 is disengaged from the fitting hole 27 upon receiving pressure of hydraulic oil supplied to at least one of the advance chamber 52 and the retard chamber 56 that are located adjacent the vane 14 b.

Due to the above configuration of the drive unit 10, while the lock pin 26 does not lock the vane rotor 14, the vane rotor 14 is rotated relative to the housing 11 in an advance direction due to supply of hydraulic oil to the advance chambers 52 to 55 and due to drain of hydraulic oil from the retard chambers 56 to 59. Thus, in the above case, a relative phase of the camshaft 2 relative to the crankshaft is changed in the advance direction, and thereby valve timing is advanced. Also, while the lock pin 26 of the drive unit 10 does not lock the vane rotor 14, the vane rotor 14 is rotated relative to the housing 11 in the retard direction due to supply of hydraulic oil to the retard chambers 56 to 59 and due to drain of hydraulic oil from the advance chambers 52 to 55. Thus, in the above situation, the phase of the camshaft 2 relative to the crankshaft is changed in the retard direction, and thereby valve timing is retarded. Furthermore, in a state, where the lock pin 26 of the drive unit 10 does not lock the vane rotor 14, if supply and drain of hydraulic oil of all the fluid chambers 52 to 59 is limited, the vane rotor 14 rotates at a speed identical with a rotational speed of the housing 11. Thus, valve timing is substantially held the same.

(Control Unit)

In the control unit 30 shown in FIG. 1, an advance output passage 72 is communicated with the advance chambers 52 to 55 regardless of an operational state of the drive unit 10, and a retard output passage 73 is communicated with the retard chambers 56 to 59 regardless of the operational state of the drive unit 10. An input communication passage 74 is communicated with a discharge port of a pump 4 serving as a “fluid input source”. The pump 4 suctions hydraulic oil from an oil pan 5 through an inlet port of the pump 4 and discharges hydraulic oil under pressure. The pump 4 of the present embodiment is a mechanical pump driven by the crankshaft, and thereby hydraulic oil is continuously introduced to the input communication passage 74 during the operation of the internal combustion engine.

A directional control valve 100 is an electric spool valve and includes a solenoid 120, a spool 130, and a return spring 140. The solenoid 120 serves as an “actuator” and generates an electromagnetic driving force. The spool 130 serves as a valve element. The return spring 140 generates a resilient restoring force. The directional control valve 100 reciprocally and straightly drives the spool 130. The directional control valve 100 includes output ports 112, 113, an intake port 114, and drain ports 115, 116. When the advance output port 112 is communicated with the advance output passage 72, it is made possible to output hydraulic oil to the advance chambers 52 to 55. When the retard output port 113 is communicated with the retard output passage 73, it is made possible to output hydraulic oil to the retard chambers 56 to 59. When the intake port 114 is communicated with the input communication passage 74, it is made possible to input hydraulic oil from the pump 4. The advance drain port 115 and the retard drain port 116 drain hydraulic oil in the directional control valve 100 to the exterior of the directional control valve 100. As above, in the directional control valve 100, the spool 130 is driven by the energization of the solenoid 120 in order to switch the mutual communication state of the ports 112 to 116.

A control circuit 200 mainly includes a microcomputer having a memory 200 a and is electrically connected with the solenoid 120 of the directional control valve 100. Also, the control circuit 200 is electrically connected with a crank sensor 202 and a cam sensor 204. The crank sensor 202 senses a rotational position of the crankshaft, and the cam sensor 204 senses a rotational position of the camshaft 2. The control circuit 200 executes computer programs stored in the memory 200 a in order to control the energization of the solenoid 120 based on output signals from each of the sensors 202, 204.

In the above control unit 30, the spool 130 of the directional control valve 100 is actuated in order to switch the mutual communication state of the ports 112 to 116 when the control circuit 200 controls the energization to the solenoid 120. As a result, when the spool 130 is displaced to a certain position, where the advance output port 112 is communicated with the intake port 114 and the retard output port 113 is communicated with the retard drain port 116, it is made possible to supply hydraulic oil from the pump 4 to the advance chambers 52 to 55 and to drain hydraulic oil from the retard chambers 56 to 59 through the retard drain port 116. Also, when the spool 130 is displaced to another position, where the advance output port 112 is communicated with the advance drain port 115 and the retard output port 113 is communicated with the intake port 114, it is made possible to supply hydraulic oil from the pump 4 to the retard chambers 56 to 59 and to drain hydraulic oil from the advance chambers 52 to 55 through the advance drain port 115. Furthermore, when the spool 130 is displaced to the other position, where the mutual communication between the ports 112 to 116 is disabled, the supply of hydraulic oil to the fluid chambers 52 to 59 and the drain of hydraulic oil from the fluid chambers 52 to 59 are both limited.

(Characteristic Part)

Characteristic parts of the valve timing adjusting apparatus 1 will be described below.

(Torque Variation)

Torque variations or torque reversals are caused to the camshaft 2 by, for example, a reaction force of a valve spring for the intake valve opened and closed by the camshaft 2 during the operation of the internal combustion engine. The generated torque variations are applied to the vane rotor 14 of the drive unit 10 through the camshaft 2. As shown in FIG. 3, torque alternately changes between (a) a negative torque that is applied to the housing 11 in the advance direction and (b) a positive torque that is applied to the housing 11 in the retard direction. It should be noted that in the torque variations, for example, a peak torque T+ of the positive torque may be substantially identical with an absolute value of a peak torque T− of the negative torque such that the average torque is substantially zero. Alternatively, the peak torque T+ of the positive torque may be greater than the absolute value of the peak torque T− of the negative torque such that the average torque is biased toward the positive torque.

(Control Unit)

As shown in FIG. 4, in the control unit 30, the directional control valve 100 includes a sleeve 110, the solenoid 120, a drive shaft 122; the spool 130, and the return spring 140.

The sleeve 110 is made of metal and has a hollow cylindrical shape, and the sleeve 110 has one end portion 110 a that is fixed to the solenoid 120. The sleeve 110 defines the advance drain port 115, the advance output port 112, the intake port 114, the retard output port 113, and the retard drain port 116 arranged in the longitudinal direction of the sleeve 110 in the above order from the one end portion 110 a to the other end portion 110 b of the sleeve 110. The end portion 110 a is positioned adjacent to the solenoid 120, and the end portion 110 b is positioned on a side of the sleeve 110 opposite from the solenoid 120.

The spool 130 is made of metal and has multiple lands thereon. The spool 130 is coaxially received in the sleeve 110. The spool 130 has one end portion 130 a that is coupled coaxially with the drive shaft 122, and the drive shaft 122 is electromagnetically driven by the solenoid 120. Due to the above configuration, the spool 130 is displaceable together with the drive shaft 122 in the longitudinal direction. The spool 130 defines an advance support land 132, an advance switch land 133, a retard switch land 134, and a retard support land 135 arranged in the above order in the longitudinal direction of spool 130 from the one end portion 130 a to the other end portion 130 b.

The advance support land 132 is always supported by a part of the sleeve 110 positioned between the advance drain port 115 and the other end portion 110 b. The advance switch land 133 is supported by at least one of (a) a part of the sleeve 110 positioned between the advance output port 112 and the advance drain port 115 and (b) another part of the sleeve 110 positioned between the advance output port 112 and the intake port 114 depending of the position of the spool 130. The retard switch land 134 is supported by at least one of (a) a part of the sleeve 110 positioned between the retard output port 113 and the retard drain port 116 and (b) another part of the sleeve 110 positioned between the retard output port 113 and the intake port 114 depending on the position of the spool 130. The retard support land 135 is always supported by a part of the sleeve 110 positioned between the retard drain port 116 and the end portion 110 a.

The return spring 140 is made of a metal compression coil spring and is coaxially received within the sleeve 110. The return spring 140 is interposed between (a) the end portion 110 b of the sleeve 110 and (b) the advance support land 132 of the spool 130. The return spring 140 generates a resilient restoring force when the return spring 140 is compressed, and the return spring 140 biases the spool 130 in the longitudinal direction toward the solenoid 120. In contrast, the solenoid 120 generates an electromagnetic driving force upon energization, and biases the spool 130 together with the drive shaft 122 in the longitudinal direction toward the return spring 140. Thereby, the directional control valve 100 actuates the spool 130 based on the balance between (a) the resilient restoring force generated by the return spring 140 and (b) the electromagnetic driving force generated by the solenoid 120, and accordingly the position of the spool 130 is changed.

Due to the above configuration, when the spool 130 is positioned at the advance position shown in FIGS. 4, 5, the advance output port 112 is communicated with the intake port 114 through a space between the advance switch land 133 and the retard switch land 134. Also, when the spool 130 is positioned at the advance position, the retard output port 113 is communicated with the retard drain port 116 through a space between the retard switch land 134 and the retard support land 135. Furthermore, when the spool 130 is positioned at the advance position, the advance switch land 133 disconnects the advance drain port 115 from all of the other ports 112 to 114, 116.

When the spool 130 is positioned at a retard position shown in FIGS. 6, 7, the retard output port 113 is communicated with the intake port 114 through a space between the retard switch land 134 and the advance switch land 133. Also, when the spool 130 is positioned at the retard position, the advance output port 112 is communicated with the advance drain port 115 through a space between the advance switch land 133 and the advance support land 132. Furthermore, when the spool 130 is positioned at the retard position, the retard switch land 134 disconnects the retard drain port 116 from all of the other ports 112 to 115.

When the spool 130 is positioned at a hold position shown in FIG. 8, the advance output port 112 is closed by the advance switch land 133, and the retard output port 113 is closed by the retard switch land 134, As a result, all the mutual communication between the ports 112 to 116 is disabled.

In addition to the above configuration, as shown in FIGS. 1, 4, the control unit 30 is provided with a relay passage 160 and communication passages 74, 170, 180 at an exterior of the directional control valve 100. Also, the communication passages 74, 170, 180 are provided with check valves 78, 172, 182, respectively.

More specifically, as shown in FIG. 4, the drain relay passage 160 provides communication between the advance drain port 115 and the retard drain port 116 and is closed to the exterior of the directional control valve 100 over the entirety of the drain relay passage 160 between the ports 115, 116. In other words, the drain relay passage 160 closes the advance drain port 115 and the retard drain port 116 relative to the exterior of the directional control valve 100. As above, the input communication passage 74 is communicated with the pump 4 and the intake port 114, and the input communication passage 74 is closed to the exterior of the directional control valve 100 over the entirety of the input communication passage 74 between the pump 4 and the intake port 114. In other words, the input communication passage 74 closes the pump 4 and the intake port 114 relative to the exterior of the valve 100.

The advance communication passage 170 is communicated with the intake port 114 through a part of the input communication passage 74 positioned between the input check valve 78 and the directional control valve 100. Also, the advance communication passage 170 is communicated with the advance drain port 115 through a part of the drain relay passage 160, the part being positioned opposite from an end of the passage 160 adjacent the retard drain port 116. Due to the above configuration, the advance communication passage 170 is closed to the exterior of the directional control valve 100 over the entirety of the passage between the intake port 114 and the advance drain port 115. In other words, the advance communication passage 170 closes the intake port 114 and the advance drain port 115 relative to the exterior of the valve 100.

The retard communication passage 180 is communicated with the intake port 114 through a part of the input communication passage 74 positioned between the input check valve 78 and the directional control valve 100. Also, the retard communication passage 180 is communicated with the retard drain port 116 through a part of the drain relay passage 160 opposite from an end of the passage 160 adjacent the advance drain port 115. Due to the above configuration, the retard communication passage 180 is closed to the exterior of the directional control valve 100 over the entirety of the passage between the intake port 114 and the retard drain port 116. In other words, the retard communication passage 180 closes the intake port 114 and the retard drain port 116 relative to the exterior of the valve 100.

The input check valve 78 is provided in the input communication passage 74 such that the input check valve 78 allows hydraulic oil to flow in a valve opening direction from the pump 4 to the intake port 114, and also the input check valve 78 limits hydraulic oil from flowing in a valve closing direction from the intake port 114 toward the pump 4. Due to the above configuration, the input check valve 78 opens when pressure in the input communication passage 74 between the input check valve 78 and the pump 4 is higher than that in the input communication passage 74 between the input check valve 78 and the intake port 114. As a result, the input communication passage 74 allows hydraulic oil to flow from the pump 4 toward the intake port 114, and thereby enables a normal flow of hydraulic oil relative to the pump 4. Also, when pressure in the input communication passage 74 between the input check valve 78 and the intake port 114 is higher than that in the input communication passage 74 between the input check valve 78 and the pump 4, the input check valve 78 is closed. As a result, the input check valve 78 restricts a backflow of hydraulic oil in the input communication passage 74 to the pump 4 from the intake port 114. In other words, the check valve 78 prevents a backflow of hydraulic oil toward the pump 4.

The advance check valve 172 is provided in the advance communication passage 170 such that the advance check valve 172 allows hydraulic oil to flow from the advance drain port 115 to the intake port 114 through the drain relay passage 160, the advance communication passage 170, and the input communication passage 74. Also, the advance check valve 172 limits hydraulic oil from flowing from the intake port 114 to the advance drain port 115. Due to the above configuration, the advance check valve 172 opens when pressure in the passages 160, 170 between the advance check valve 172 and the advance drain port 115 is higher than that in the passage 170, 74 between the advance check valve 172 and the intake port 114. As a result, the advance check valve 172 allows hydraulic oil to flow in the advance communication passage 170 from the advance drain port 115 to the intake port 114. Also, the advance check valve 172 is closed when pressure in the passages 74, 170 between the advance check valve 172 and the intake port 114 is higher than pressure in the passages 160, 170 between the advance check valve 172 and the advance drain port 115. As a result, the advance check valve 172 limits flow of hydraulic oil in the advance communication passage 170 from the intake port 114 to the advance drain port 115.

The retard check valve 182 is provided in the retard communication passage 180 such that the retard check valve 182 allows hydraulic oil to flow in a valve opening direction from the retard drain port 116 to the intake port 114 through the drain relay passage 160, the retard communication passage 180, and the input communication passage 74. Also, the retard check valve 182 limits flow of hydraulic oil in a valve closing direction from the intake port 114 to the retard drain port 116. Due to the above configuration, the retard check valve 182 opens when pressure in the passages 160, 180 between the retard check valve 182 and the retard drain port 116 is higher than pressure in the passages 74, 180 between the retard check valve 182 and the intake port 114. As a result, the retard check valve 182 allows hydraulic oil to flow in the retard communication passage 180 from the retard drain port 116 to the intake port 114. Also, the retard check valve 182 is closed when pressure in the passages 74, 180 between the retard check valve 182 and the intake port 114 is higher than pressure in the passages 160, 180 between the retard check valve 182 and the retard drain port 116. As a result, the retard check valve 182 limits flow of hydraulic oil through the retard communication passage 180 from the intake port 114 to the retard drain port 116.

(Operation for Adjusting Valve Timing)

During the operation of the internal combustion engine, in which the pump 4 is driven, the control circuit 200 computes an actual phase and a target phase range of the valve timing based on output signals from each of the sensors 202, 204. Then, the control circuit 200 controls the electric current for energizing the solenoid 120 of the directional control valve 100 in order to displace the spool 130 of the directional control valve 100 based on the computation results of the above phases. Due to the above, hydraulic oil is supplied to or drained from each of the fluid chambers 52 to 59 in response to the position of the spool 130 of the directional control valve 100, and thereby the valve timing is adjusted within the target phase range.

The valve timing adjustment operation by the valve timing adjusting apparatus 1 will be detailed below.

(1) Advance Operation

Firstly, the advance operation will be described, in which the vane rotor 14 is rotated relative to the housing 11 in the advance direction such that valve timing is advanced.

When an advance operation condition is established, which indicates an off state of acceleration of the internal combustion engine or a low/intermediate speed and high load operational state, the control circuit 200 sets a target direction as the advance direction in order to execute a timing advance process. In the above, the target direction indicates a direction for rotating the vane rotor 14 relative to the housing 11. In the timing advance process, the electric current for energizing the solenoid 120 is set at a predetermined value I1 such that the spool 130 is driven to the advance position shown in FIGS. 4, 5. In the present embodiment, the predetermined value I1 is a maximum value I1. Due to the above, the communication between the advance output port 112 and the intake port 114 is established, and the communication between the retard output port 113 and the retard drain port 116 is also established in the directional control valve 100. Also, the output ports 112, 113 are both disconnected from the advance drain port 115 in the directional control valve 100.

In a case, where the spool 130 is positioned at the advance position that realizes the above communication/discommunication state, when the negative torque is applied to the vane rotor 14 such that the retard chambers 56 to 59 are compressed, as shown in FIG. 4, hydraulic oil in the retard chambers 56 to 59 is drained to the retard drain port 116 through the retard output passage 73 and the retard output port 113 in this order. Part of oil drained to the retard drain port 116 flows into the retard communication passage 180 between the retard drain port 116 and the intake port 114. Thus, when pressure in the passages 160, 180 between the retard check valve 182 and the retard drain port 116 is higher than pressure in the passages 74, 180 between the retard check valve 182 and the intake port 114, the check valve 182 opens. Due to the above, as shown in FIG. 4, hydraulic oil flows into the intake port 114 through the retard communication passage 180, and is further supplied to the advance chambers 52 to 55 through the advance output port 112.

Also, the other part of oil drained from the retard chambers 56 to 59 to the retard drain port 116 flows into the drain relay passage 160 that provides communication between the retard drain port 116 and the advance drain port 115 as shown in FIG. 4. The oil that has been introduced into the drain relay passage 160 further flows into the advance communication passage 170 that provides communication between the advance drain port 115 and the intake port 114. Thus, when pressure in the passages 160, 170 between the advance check valve 172 and the advance drain port 115 becomes higher than pressure in the passages 74, 170 between the advance check valve 172 and the intake port 114, the check valve 172 opens. Due to the above, as shown in FIG. 4, hydraulic oil is capable of flowing into the intake port 114 through the advance communication passage 170. Thus, the other part of the drained oil is also supplied to the advance chambers 52 to 55 through the advance communication passage 170.

As above, hydraulic oil that has flown through the communication passage 170 flows through the input communication passage 74 before the hydraulic oil reaches the intake port 114. Also, hydraulic oil that has flown through the communication passage 180 flows through the input communication passage 74 before reaching the intake port 114. When pressure in the input communication passage 74 between the input check valve 78 and the intake port 114 becomes higher than pressure in the input communication passage 74 between the input check valve 78 and the pump 4, the input check valve 78 is closed, and thereby flow of hydraulic oil toward the pump 4 is limited. Due to the above, hydraulic oil that is intended to be supplied from the retard chambers 56 to 59 to the advance chambers 52 to 55 is limited from flowing back to the pump 4. Also, in contrast, even when pressure in the input communication passage 74 between the input check valve 78 and the pump 4 becomes higher than pressure in the input communication passage 74 between the input check valve 78 and the intake port 114 due to the possible leakage of hydraulic oil to the exterior, the input check valve 78 opens. Due to the above, both (a) hydraulic oil that has passed through each of the communication passages 180, 170 and (b) hydraulic oil discharged from the pump 4 are made flow into the intake port 114 and the advance output port 112 sequentially. As a result, shortage of flow of the hydraulic oil that is supplied to the advance chambers 52 to 55 is limited.

As a result, when the negative torque is applied, it is possible to supply hydraulic oil in the retard chambers 56 to 59 to the advance chambers 52 to 55 that are increased in volume due to the application of the negative torque. The above hydraulic oil supply may employ a route that passes through the retard communication passage 180 and may alternatively employ another route that passes through the drain relay passage 160 and the advance communication passage 170. In the above configuration, each of the communication passages 74, 180, 170 and the drain relay passage 160 is closed relative to or disconnected from the exterior of the directional control valve 100, and also the advance drain port 115 that is communicated with the advance communication passage 170 is closed to each of the output ports 112, 113. As a result, the employing of both the above routes makes it possible to supply a large amount of hydraulic oil to the advance chambers 52 to 55 without the leakage of hydraulic oil in the retard chambers 56 to 59 to the exterior of the directional control valve 100. Due to the above, even in a case, where cross sectional areas or passage areas of the retard communication passage 180 and the advance communication passage 170 are reduced, the sufficient amount of hydraulic oil supplied to the advance chambers 52 to 55 is achieved. Therefore, it is possible to reduce in size valve elements of the check valves 182, 172 provided in the communication passages 180, 170, respectively, in order to achieve the high timing advance responsivity.

As shown in FIG. 5, in the advance position, when the positive torque is applied to the vane rotor 14 and thereby hydraulic oil in the advance chambers 52 to 55 is compressed, hydraulic oil in the advance chambers 52 to 55 leaks to the intake port 114 through the advance output passage 72 and the advance output port 112 sequentially. Furthermore, the oil leaked to the intake port 114 flows through the input communication passage 74 and then flows into both the retard communication passage 180 and the advance communication passage 170. Due to the above, pressure in the passages 160, 180 between the retard the check valve 182 and the retard drain port 116 becomes lower than pressure in the passages 180, 74 between the check valve 182 and the intake port 114. Also, pressure in the passages 170, 160 between the advance the check valve 172 and the advance drain port 115 becomes lower than pressure in the passages 170, 74 between the advance the check valve 172 and the intake port 114. As a result, the check valves 182, 172 are closed. Accordingly, hydraulic oil is limited from reaching the retard drain port 116 and the advance drain port 115 that is connected with the retard drain port 116. Therefore, backflow of hydraulic oil in the advance chambers 52 to 55 to the retard chambers 56 to 59 through the retard drain port 116 and the retard output port 113 is limited.

Also, as shown in FIG. 5, because oil leaks from the advance chambers 52 to 55 through the intake port 114 and flows into the input communication passage 74, pressure in the passage 74 between the input check valve 78 and the intake port 114 becomes higher than pressure in the passage 74 between the input check valve 78 and the pump 4. Accordingly, the input check valve 78 is closed. As a result, it is possible to limit the backflow of hydraulic oil in the advance chambers 52 to 55 to the pump 4.

(2) Retard Operation

Next, the retard operation will be described below, in which the vane rotor 14 is rotated relative to the housing 11 in the retard direction such that valve timing is retarded.

When a retard operation condition is established, which indicates a normal operational state, such as a low load operation of the internal combustion engine, the control circuit 200 sets the target direction as the retard direction for rotating the vane rotor 14 relative to the housing 11 such that the control circuit 200 executes the timing retard process. In the timing retard process, the electric current for energizing the solenoid 120 is set at a value I2, which is smaller than the value I1 used during the timing advance process, in order to displace the spool 130 to the retard position shown in FIGS. 6, 7. In the present embodiment, the value I2 is a minimum value I2. Due to the above, the communication between the advance output port 112 and the advance drain port 115 is established, and also the communication between the retard output port 113 and the intake port 114 is established in the valve 100. Also, the output ports 112, 113 are both disconnected from the retard drain port 116 in the valve 100.

In a state, where the spool 130 is positioned at the retard position that realizes the above communication/discommunication state, when the positive torque is applied to the vane rotor 14 and thereby the advance chambers 52 to 55 are compressed, as shown in FIG. 6, hydraulic oil in the advance chambers 52 to 55 is drained to the advance drain port 115 through the advance output passage 72 and the advance output port 112 sequentially. The check valve 172 opens when part of oil drained to the advance drain port 115 flows into the advance communication passage 170 that provides communication between the advance drain port 115 and the intake port 114, and thereby pressure in the passages 170, 160 between the advance the check valve 172 and the advance drain port 115 becomes higher than pressure in the passages 170, 74 between the advance the check valve 172 and the intake port 114. Due to the above, as shown in FIG. 6, hydraulic oil flows into the intake port 114 through the advance communication passage 170, and further is supplied to the retard chambers 56 to 59 through the retard output port 113.

Also, the other part of the oil drained from the advance chambers 52 to 55 to the advance drain port 115 flows into the drain relay passage 160 that provides communication between the advance drain port 115 and the retard drain port 116 as shown in FIG. 6. Thus, the oil that has been introduced into the drain relay passage 160 flows through the retard communication passage 180 that provides communication between the retard drain port 116 and the intake port 114, and thereby pressure in the passages 180, 160 between the retard the check valve 182 and the retard drain port 116 becomes higher than pressure in the passage 180, 74 between the retard the check valve 182 and the intake port 114, accordingly. Thus, the check valve 182 opens. Due to the above, as shown in FIG. 6, because hydraulic oil flows into the intake port 114 through the retard communication passage 180, the other part of the drained oil from the advance chambers 52 to 55 is also supplied to the retard chambers 56 to 59.

Hydraulic oil that has passed through the communication passage 170 reaches the intake port 114 through the input communication passage 74. Also, hydraulic oil that has passed through the communication passage 180 reaches the intake port 114 through the input communication passage 74. Similar to the case, where the negative torque is applied in the advance operation, when pressure in the passage 74 between the input check valve 78 and the intake port 114 becomes higher than pressure in the passage 74 between the input check valve 78 and the pump 4, the input check valve 78 is closed, and thereby limits the flow of hydraulic oil toward the pump 4. Due to the above, it is possible that leaked oil from the advance chambers 52 to 55 is successfully supplied to the retard chambers 56 to 59 without flowing back to the pump 4. Also, when pressure in the input communication passage 74 between the input check valve 78 and the pump 4 becomes higher than pressure in the passage 74 between the input check valve 78 and the intake port 114 due to the possible leakage of hydraulic oil to the exterior, the input check valve 78 opens similar to the case, where the negative torque is applied in the advance operation. As above, because hydraulic oil discharged from the pump 4 flows into the intake port 114 and the retard output port 113 sequentially and the hydraulic oil passing through the communication passages 170, 180 also flows into the intake port 114 and the retard output port 113, it is possible to avoid the shortage of hydraulic oil supplied to the retard chambers 56 to 59.

As above, when the positive torque is applied, it is possible to supply hydraulic oil in the advance chambers 52 to 55 to the retard chambers 56 to 59 that are increased in volume due to the application of the positive torque. The above hydraulic oil supply may employ a route that passes through the advance communication passage 170 and may alternatively employ another route that passes through the drain relay passage 160 and the retard communication passage 180. In the above, each of the communication passages 74, 170, 180 and the drain relay passage 160 is closed to or disconnected from the exterior of the directional control valve 100, and the retard drain port 116 that is communicated with the retard communication passage 180 is disconnected from the output ports 112, 113 in the valve 100. Thereby, the employing of both the above routes makes it possible to supply hydraulic oil in the advance chambers 52 to 55 to the retard chambers 56 to 59 by a substantially large amount of hydraulic oil without the leakage of hydraulic oil to the exterior of the directional control valve 100. Due to the above, it is possible to achieve the sufficient amount of hydraulic oil supplied to the retard chambers 56 to 59 even when the cross sectional areas of the advance communication passage 170 and the retard communication passage 180 are reduced. Thus, it is possible to reduce in size the valve elements of the check valves 172, 182 provided in the communication passages 170, 180 in order to increase the timing retard responsivity.

As shown in FIG. 7, in a case, where the spool 130 is positioned at the retard position, when the negative torque is applied to the vane rotor 14 and thereby the retard chambers 56 to 59 are compressed, hydraulic oil in the retard chambers 56 to 59 leaks to the intake port 114 through the retard output passage 73 and the retard output port 113 sequentially. Furthermore, oil leaked to the intake port 114 flows into both the advance communication passage 170 and the retard communication passage 180 through the input communication passage 74. Due to the above, when pressure in the passages 170, 160 between the advance the check valve 172 and the advance drain port 115 becomes lower than pressure in the passages 170, 74 between the advance the check valve 172 and the intake port 114 and also when pressure in the passages 180, 160 between the retard the check valve 182 and the retard drain port 116 becomes lower than pressure in the passages 180, 74 between the retard the check valve 182 and the intake port 114, each of the check valves 172, 182 is closed. Then, hydraulic oil is limited from reaching the advance drain port 115 and the retard drain port 116 that is communicated with the advance drain port 115. Due to the above, it is possible to limit hydraulic oil in the retard chambers 56 to 59 from backflowing into the advance chambers 52 to 55 through the advance drain port 115 and the advance output port 112.

Also, as shown in FIG. 7, the oil leaked from the retard chambers 56 to 59 to the intake port 114 flows into the input communication passage 74. As a result, similar to the case, where the positive torque is applied in the advance operation, pressure in the input communication passage 74 between the input check valve 78 and the intake port 114 becomes higher than the pressure in the passage 74 between the input check valve 78 and the pump 4, and thereby the input check valve 78 is closed. Accordingly, it is possible to limit the backflow of hydraulic oil in the retard chambers 56 to 59 to the pump 4.

(3) Hold Operation

The hold operation will be described below, in which the valve timing is kept substantially unchanged, and also the vane rotor 14 is not rotated relative to the housing 11.

When a hold operation condition is established, which indicates a stable operational state, such as an unchanged position of the acceleration pedal of the internal combustion engine, the control circuit 200 executes a hold process. In the hold process, the electric current for energizing the solenoid 120 is set at an intermediate value I3 in order to drive the spool 130 to the hold position shown in FIG. 8. In the above, the intermediate value I3 is in a range between the value I1 for the timing advance process and the value I2 for the timing retard process, for example. Due to the above, the spool 130 closes the output ports 112, 113, and the mutual communication between all the ports 112 to 116 is disabled.

When the spool 130 is positioned at the hold position that enables the above totally disconnected state, the supply of hydraulic oil to the fluid chambers 52 to 59 and the drain of hydraulic oil from the fluid chambers 52 to 59 are both restricted, and thereby it is possible to reliably hold the valve timing within the target phase range.

In the valve timing adjusting apparatus 1 of the above embodiment, it is possible to quickly and appropriately adjust the valve timing in accordance with the operational state of the internal combustion engine.

Other Embodiment

The interpretation of the present invention is not limited to the above embodiment. However, the present invention is applicable to various embodiments provided that the various embodiments do not deviate from the gist of the present invention.

Specifically, in the directional control valve 100 of the control unit 30, the solenoid 120 serving as an “actuator” may be replaced by, for example, a piezoactuator or an oil pressure actuator. Also, in the directional control valve 100, the output port 113 may be alternatively communicated with the advance chambers 52 to 55 through the advance output passage 72, and the output port 112 may be alternatively communicated with the retard chambers 56 to 59 through the retard output passage 73.

In the control unit 30, both of the advance communication passage 170 and the retard communication passage 180 may be directly communicated with the intake port 114, alternatively. Also, the advance communication passage 170 and the retard communication passage 180 may be directly communicated with the advance drain port 115 and the retard drain port 116, respectively. Also, in the control unit 30, the input communication passage 74 may be alternatively communicated with the intake port 114 through at least one of the advance communication passage 170 and the retard communication passage 180. Also, the drain relay passage 160 may be communicated with the advance drain port 115 and the retard drain port 116 through the advance communication passage 170 and the retard communication passage 180, respectively.

The drive unit 10 may be provided with, for example, a resilient body, such as an assist spring, and the resilient body biases the camshaft 2 in a direction opposite from the direction, in which the average torque of the torque variations is biased. Also, in the drive unit 10, the vane rotor 14 may alternatively serve as a “driving-side rotor” and may be rotated synchronously with the crankshaft, and the housing 11 may alternatively serve as a “driven-side rotor” and may be rotated synchronously with the camshaft 2.

Then, the present invention may be applied to an apparatus that adjusts valve timing of an exhaust valve serving as a “valve”, and may be applied to another apparatus that adjusts valve timing of both the intake valve and the exhaust valve.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A valve timing adjusting apparatus for adjusting valve timing of a valve that is opened and closed by a camshaft through torque transmission from a crankshaft of an internal combustion engine, the valve timing adjusting apparatus comprising: a driving-side rotor that is rotatable synchronously with the crankshaft; a driven-side rotor that is rotatable synchronously with the camshaft, wherein: the driven-side rotor and the driving-side rotor define therebetween an advance chamber and a retard chamber arranged one after another in a rotational direction, and when working fluid is supplied to the advance chamber or the retard chamber, the driven-side rotor is rotated relative to the driving-side rotor in an advance direction or a retard direction; a control unit that controls supply of working fluid to the advance chamber and the retard chamber, wherein, the control unit includes a directional control valve, an advance communication passage, an advance check valve, a retard communication passage, a retard check valve, and a drain relay passage; the directional control valve includes: an intake port, through which the directional control valve receives working fluid from an external fluid input source; an advance output port, through which the directional control valve outputs working fluid to the advance chamber; a retard output port, through which the directional control valve outputs working fluid to the retard chamber; an advance drain port, through which the directional control valve drains working fluid; and a retard drain port, through which the directional control valve drains working fluid; the driven-side rotor is rotated relative to the driving-side rotor in the advance direction when the followings are satisfied: the directional control valve provides communication between the advance output port and the intake port; the directional control valve provides communication between the retard output port and the retard drain port; and the directional control valve disconnects the advance output port and the retard output port from the advance drain port; the driven-side rotor is rotated relative to the driving-side rotor in the retard direction when the followings are satisfied; the directional control valve provides communication between the advance output port and the advance drain port; the directional control valve provides communication between the retard output port and the intake port; and the directional control valve disconnects the advance output port and the retard output port from the retard drain port; the advance communication passage is provided at an exterior of the directional control valve and is communicated with the advance drain port and the intake port; the advance communication passage closes the advance drain port and the intake port relative to the exterior of the directional control valve; the advance check valve is provided in the advance communication passage; the advance check valve allows working fluid to flow from the advance drain port toward the intake port and limits working fluid from flowing from the intake port toward the advance drain port; the retard communication passage is provided at the exterior of the directional control valve and is communicated with the retard drain port and the intake port, the retard communication passage closes the retard drain port and the intake port relative to the exterior of the directional control valve, the retard check valve is provided in the retard communication passage; the retard check valve allows working fluid to flow from the retard drain port toward the intake port and limits working fluid from flowing from the intake port toward the retard drain port; the drain relay passage is provided at the exterior of the directional control valve and is communicated with the advance drain port and the retard drain port; and the drain relay passage closes the advance drain port and the retard drain port relative to the exterior of the directional control valve.
 2. The valve timing adjusting apparatus according to claim 1, wherein; the control unit further includes: an input communication passage that is provided at the exterior of the directional control valve, wherein the input communication passage provides communication between the fluid input source and the intake port and closes the fluid input source and the intake port relative to the exterior of the directional control valve; and an input check valve that is provided in the input communication passage, wherein the input check valve allows working fluid to flow from the fluid input source toward the intake port and limits working fluid from flowing from the intake port toward the fluid input source; and the advance communication passage and the retard communication passage are communicated with the intake port through a part of the input communication passage, the part being positioned between the input check valve and the directional control valve.
 3. The valve timing adjusting apparatus according to claim 1, wherein: the directional control valve further includes a spool and an actuator; the spool is reciprocably displaceable between an advance position and a retard position; when the spool is at the advance position, the followings are satisfied: the spool provides communication between the advance output port and the intake port; the spool provides communication between the retard output port and the retard drain port; and the spool disconnects the advance output port and the retard output port from the advance drain port; when the spool is at the retard position, the followings are satisfied: the spool provides communication between the advance output port and the advance drain port; the spool provides communication between the retard output port and the intake port; and the spool disconnects the advance output port and the retard output port from the retard drain port; the actuator displaces the spool to the advance position in order to rotate the driven-side rotor relative to the driving-side rotor in the advance direction; and the actuator displaces the spool to the retard position in order to rotate the driven-side rotor relative to the driving-side rotor in the retard direction. 